This issue keeps appearing in online forums. Many laser/IPL operators talk about ‘lots of hair growth’ usually after a few sessions.
So, I investigated this with my computer model. I had developed this model a few years ago to look at the ‘best’ time intervals between repeat treatments.
Last year, while researching laser/IPL treatment of hair with a wide range of devices (including home-use IPLs – that’s another post…), I discovered that clinical researchers had found that thermally ‘injured’ anagen follicles will go into the catagen phase almost immediately. This occurs regardless of at what point in the anagen phase they were.
This is very interesting. It means that laser/IPL-induced thermal damage will force many follicles into catagen, if those follicles are not completely denatured (destroyed). This, of course, happens when the applied fluence is too low. The energy will denature some of the germ cells, but leave a sufficient quantity behind to allow for the regrowth of that follicle, after it goes through the subsequent catagen-telogen phases again.
This will occur after every laser/IPL treatment, meaning that many follicles will be forced out of their natural growth cycle. As a consequence, their growth patterns are completely disrupted.
When I plugged this into my computer model, I found that synchronised growth will naturally occur after about 7 sessions (see graph – this represents the hairs in the underarm area). We can see that the percentage of ‘live’ follicles drops dramatically after the first session – something which almost everyone can confirm.
Then there is not much change in the overall number of live, visible follicles until after session 4, where the percentages drop from around 40 to 20. After session 7, we see a rise in the number of live, visible follicles – the percentage jumps back up to nearly 50%!!
To the human eye, this appears to be a significant jump in the number of hairs – from around 20 to 50% appears to be a “lot” of growth. Don’t forget, this occurs months after the first session – the memory of the original number of hairs has long faded!
Why does this happen?
Well, it’s all down to the fact that follicles are essentially ‘forced’ into catagen phase, if they are damaged. This occurs with any treatment which damages hair follicles – not just laser/IPL. Plus, it occurs afters EVERY treatment session with laser and/or IPL. So many follicles are repeatedly being forced into anagen, out of their natural cycle! Their typical growth cycle is completely disrupted by this process.
Conclusion
Synchronised hair growth is a real thing!! It will happen simply because of the way follicles respond to treatments. I assume it is much more obvious in some people than in others, and in some body areas than in others too, but it is observed with great regularity.
The good news is that when all those follicles are in anagen, they are easy to treat. The ‘best’ time to kill follicles is in early anagen, before the bulb descends too deeply into the dermis. I am working on this at the moment and plan to publish a paper on it soon.
Hope this clears up some confusion,
Mike.
Mike Murphy's Blog 